The present invention relates to a glass-ceramic composite with excellent properties used as electric-insulating ceramic material for high frequency insulators, IC packages, and multilayer substrates, etc.
Alumina with large insulating capacity is generally used as electric-insulating material for substrates of electronic parts and segments. Alumina substrates, however, fail to attain sufficient properties while high-speed and greater scale semi-conductor chips are developed. Alumina substrates have relatively large permittivity and a greater thermal expansion coefficient than semi-conductor chips, thus causing delay in signal propagation and stress applied onto semi-conducting chips.
Although low resistance conductors such as gold, silver, and copper are preferable for substrates of semi-conductor chips, these conductor metals with low melting points have not actually been used since only metals with high melting points are applicable to alumina substrates fired at high temperatures.
Low temperature-fired substrates have recently been developed in order to solve the above problem; such substrates are broadly classified into two groups, that is, glass composite and crystallized glass.
Examples of the glass composite include: alumina with given amounts of alkaline earth metals and other additives (Japanese Published Unexamined Patent Application No. H2-149464); alumina with glass powder having a predetermined specific surface area (Japanese Published Unexamined Patent Application No. S62-113758); and glass composition including hard powder forming a specified crystal phase (Japanese Published Unexamined Patent Application No. H2-225338).
The crystallized glass is: for example, a crystallized glass body with low permittivity and a small thermal expansion coefficient (Japanese Published Examined Patent Application No. S63-31420); or crystallized glass with ceramic particles dispersed therein and covered with silicon dioxide (Japanese Published Examined Patent Application No. S63-6503).
Neither the glass composite nor the crystallized glass mentioned above are, however, not perfect nor sufficient as substrate material. The glass composites have insufficient strength, lack of dimensional precision, and large dielectric loss, and the crystallized glass bodies have the following problems.
The crystallized glass body with low permittivity and a small thermal expansion coefficient has strength as low as 2,000 kg/cm.sup.2 and a very small thermal expansion coefficient of 16 to 26.times.10.sup.-7, thus being not applicable to IC packages, which require joints of terminals or other metal parts and hermetic seals. When the substrate has insufficient strength and a very small thermal expansion coefficient, junction with brazing or glass may cause cracks on the substrate.
On the other hand, simple substance of the crystallized glass requires long-time firing for sufficient strength, thus consuming labor, time, and money. Moreover, the material for it is quite expensive.